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Abstract

Light-emitting diode (LED) video displays enclose thousands of LEDs
which create the resulting image. LED intensity is regulated using pulse width
modulation (PWM). Though the individual LED current is small, the total current
consumed is large. Simultaneous switching of a large number of LEDs dimmed
by PWM can cause serious electromagnetic interference (EMI). Three LED PWM
dimming techniques have been studied for potential EMI. Techniques represent
different current pulse positioning in time: the aim of study was to compare
the spectrum of current produced in LED video display power supply circuits
when discussed techniques are used for pixel intensity control. It was assumed
that the produced EMI is proportional to the power supply current. The power
supply filter and transient load decoupling capacitors were not taken into
account. The uniform and nonuniform pixels' intensities distribution within
an image were assumed. Spectrum has been studied on a single pixel and the
video display tile containing 16×32 LEDs. Resulting time diagrams and frequency responses are presented.
The results indicate that, despite expected significant advantage of binary
PWM methods, in realistic case all methods' performance is similar.

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